1. FIELD OF THE INVENTION
This invention relates to the field of mass storage devices and in particular to a method and apparatus for media defect management of a rotating media storage system.
2. BACKGROUND ART
Mass storage for computer systems may be provided by rotating media storage systems, such as floppy disks, Winchester hard disks or optical disks. In a rotating media storage system, concentric or spiral "tracks" are defined on the surface of the media for storing data. Each track is divided into a number of "sectors" that provide a logical division for storing blocks of data. Each sector represents a number of bits of the data track.
When a recording media is manufactured, such as a magnetic media disk or a magneto optic media disk, tracks and sectors are defined on the disk's surface. The disk is then tested by the manufacturer to determine the validity of each sector. Media defects introduced during the manufacturing process can damage a sector so that data cannot be stored or retrieved from that sector.
Those defective sectors are identified by the manufacturer in a list so that the sectors can be avoided during operation of the disk drive. A list of the bad sectors, known as a "primary defect list" (PDL) or "manufacturers defect list" is stored on the disk media at a location that is reserved on the disk for the list. This reserved location is usually an area on the disk surface outside the boundaries of the data tracks.
When the disk media is placed into service, additional sectors on the disk may become defective. Such defective sectors are known as secondary defects or "grown" defects. A list of grown defects is maintained and stored on a disk surface. This list, known as the "secondary defect list" (SDL), is also stored at a location on the disk surface reserved for that list.
When a disk drive incorporating the disk is powered up, the primary defect list and secondary defect list are read from the disk surface and stored in random access memory (RAM). The disk controller (a microprocessor or other processing means built into the disk drive) uses the information in the PDL and SDL to avoid writing data to bad sectors. In the prior art, the disk controller uses two schemes to avoid and compensate for defective sectors. The first scheme, known as "sector slipping" is used to compensate for manufacturer's defects. The second scheme, known as linear displacement, is used to compensate for grown defects.